1. Field of the Invention
The present invention relates to an anilox offset printing unit with a short inking device. The inking device is mounted between side walls and includes a screen roller which can be doctored and can be immersed in an ink container, an inking roller, and a plate cylinder for inking a rubber blanket cylinder, wherein the plate cylinder interacts with a damping device.
2. Description of the Related Art
Anilox offset short inking devices of the above-described type do not have zone screws, but a fixedly mounted screen roller which can be doctored, so that the quantity of ink to be transferred can no longer be influenced directly. The quantity of ink to be transferred depends primarily on the type of the screen of the screen roller, and on the physical properties of the ink which is being used.
Tests have shown that the transfer width from the inking roller to the screen roller also influences the ink transfer, so that metering of the quantity of ink can be influenced by the width of the contact zones between the rollers. In addition, the transfer width from the inking roller to the plate cylinder influences the emulsifying behavior of the ink. The compulsive forces between the rollers, the quantity of damping agent emulsified into the ink, and the amount of damping agent required for being able to print without tint, all increase as the transfer width increases.
With increasing operating time of the machine, the temperature increase caused, inter alia, by the squeezing or pressing work of the rollers of the inking device, leads to a thermal expansion of the machine. The transfer widths of the inking roller to the plate cylinder and to the screen roller change as a result and deviate from the adjusted desired values.
The temperature increase of the machine additionally causes an increase of the temperature of the ink, so that the physical properties of the ink change. Among other changes, the tendency to emulsify increases, so that it is necessary to keep small the mechanical values which influence the formation of emulsions, i.e., primarily the squeezing or pressing forces in the gap between the inking roller and the plate cylinder.
British patent no. 620,148, which generally relates to an inking device of a printing machine, deals with the problem of the influence on the ink properties caused by a temperature increase. To take this value into consideration, British patent 620,148 proposes to change the gap between an ink well roller and the ink accepting roller. The change of the distance between the rollers is effected by means of an eccentric support of the ink accepting roller. Since the results of such a subsequent control can be checked only during the production sequence, variations of the ink on the print carrier are almost inevitable. In addition, the supply of damping agent is not taken into consideration when the ink properties are changed because an ink density regulation by changing the transfer width independently of the temperature is not being considered. Thus, the possibility of adjustment proposed in British patent 620,148 does not provide a solution for changing the transfer width of the inking roller to the screen roller and/or the inking roller to the plate cylinder.